Crash sensor

ABSTRACT

An improved sensor assembly for actuating a vehicle safety apparatus upon the occurrence of an accident includes a mass which is movable from an initial position to an actuated position in response to the occurrence of an accident. When the mass is in its actuated position, the safety apparatus is activated to protect the occupant of the vehicle. A plurality of spring contact fingers bias the mass toward its initial position. Cam means is associated with the contact fingers and act to apply a preload to the mass. As the mass moves toward its actuated position, the number of spring fingers which cooperate to bias the mass decreases and the biasing force exerted by the remaining spring fingers increases. Thus, the mass moves from its initial position to its actuated position against a biasing force which may be controlled by the configuration of the spring fingers and the cam member.

United States Patent Kaiser 15] 3,673,367 [451 June 27, 1972 [54] CRASH SENSOR [21] Appl. No.: 86,683

Related U.S. Application Data [52] U.S. Cl. [51 Int. Cl. [58] Field of Search ..200/61.45 R, 280/150 AB ..H0lh 35/14 ..200/61.45 R, 61.45 M, 61.53

Primary Examiner-Robert K. Schaefer Assistant Examiner-M. Ginsburg Anorney-Yount and Tarolli 57 ABSTRACT An improved sensor assembly for actuating a vehicle safety apparatus upon the occurrence of an accident includes a mass which is movable from an initial position to an actuated position in response to the occurrence of an accident. When the mass is in its actuated position, the safety apparatus is ac tivated to protect the occupant of the vehicle. A plurality of spring contact fingers bias the mass toward its initial position. Cam means is associated with the contact fingers and act to apply a preload to the mass. As the mass moves toward its actuated position, the number of spring fingers which cooperate to bias the mass decreases and the biasing force exerted by the remaining spring fingers increases. Thus, the mass moves from 56 R f hd its initial position to its actuated position against a biasing l e "mus Cl force which may be controlled by the configuration of the UNITED STATES PATENTS spring fingers and the cam member.

3,588,401 6/1971 Berryman ..200/61 .48 8 Claims, 7 Drawing Figures 30 72a 9/ iiii7l77ii? I I I I I I 0 7L ||||IIu I 5 a 1 Va 5 I 84 q; .I-nunun' l K 1L 3 i I I J CRASH SENSOR This application is a continuation-in-part of copending U.S. application, Ser. No. 814,132, filed Apr. 7, 1969, now U.S. Pat. No. 3,618,117, issued Nov. 2, 1971, which in itself is a continuation-in-part of copending U.S. application, Ser. No. 753,948, filed Aug. 20, 1968, now U.S. Pat. No. 3,552,768, issued Jan. 5, I971.

The present invention relates to a sensor assembly for actuating a vehicle safety apparatus and, more particularly, to a sensor assembly which has a mass movable against a plurality of spring fingers whose spring rates change as the mass moves to actuate the safety apparatus in response to the occurrence of an accident, so that the biasing force applied to the mass by the spring-fingers increases at a decreasing rate as the mass moves toward a position in which actuation of the safety apparatus is effected. 7

Certain known sensors which utilize a spring to bias the mass require a force of a predetermined magnitude to overcome the spring force and effect movement of the mass from its initial position to its actuated position. However, as the mass moves toward its actuated position, the force with which the biasing means biases the mass toward the initial position generally increases due to the characteristics of the spring. The desirability of having the mass subjected to a constant force as it moves has been disclosed in application, Ser. No. 8 14,132, assigned to the assignee of the present invention, and the desirability of having the mass subjected to a decreasing force has been disclosed in the Berryman application, Ser. No. 850,267, filed Aug. 14,1969, now U.S. Pat. No. 3,588,401, issued June 28, I971, assigned to the assignee of the present invention. The present invention, however, is directed to having a plurality of spring fingers applying a biasing force which increases at a decreasing rate as the mass moves to its actuated position.

Accordingly, an object of thepresent invention is to provide a new and improved sensor assembly which includes a housing, a mass located in the housing and movable from an initial position to an actuated position in response to an impulse of a predetermined magnitude imposed on the housing, a plurality of spring fingers for biasing the mass toward its initial position I and which applies a force to the mass which increases at a decreasing rate as the mass moves toward its actuated position.

A further object of the present invention is to provide a new and improved sensor assembly for actuating a safety device on a vehicle upon the occurrence of an accident and which includes a mass movable from an initial position to an actuated position upon the occurrence of an accident, a plurality of spring fingers which bias the mass when the mass moves in different directions, and a cam which acts to bend the spring fingers toward the mass when the mass is in the initial position to thereby apply a preload or biasing force to the mass.

Another object of the present invention is to provide a new and improved sensor assembly as defined in the next preceding paragraph wherein the force applied by the aggregate of spring fingers increases at a decreasing rate as the mass moves toward its actuated position.

Still another object of the present invention is the provision of a new and improved safety apparatus for protecting an occupant of a vehicle and including a confinement having a collapsed condition and an expanded condition in which the confinement restrains movement of the occupant, a source of fluid for effecting expansion of the confinement upon the occurrence of an accident, explosive means for activating the source of fluid, and a sensor assembly having a mass which moves from an initial position to an actuated position in which the mass effects actuation of the explosive means upon the occurrence of an accident and wherein the mass when in its initial position effects grounding of both sides of the explosive means so that inadvertent actuation of the explosive means due to radio frequency interference or induced currents in the circuitry does not occur.

Further objects and advantages of the present invention will become more apparent upon consideration of the following description taken in connection with drawings wherein:

FIG. I is an illustration showing a safety apparatus constructed in accordance with the present invention and associated with an automotive vehicle;

FIG. 2 is a side view illustration of a sensor assembly for detecting the occurrence of an accident and effecting activation of the safety apparatus from a collapsed condition, shown in solid lines in FIG. 1;

FIG. 3 is a plan view, taken along the line 3-3 of FIG. 2, illustrating the sensor in an active or initial condition in which resilient contact fingers bias the mass to an initial position;

FIG. 4 is a side view illustrating in solid lines the sensor in an activated condition in which the mass has moved to an actu ated position in which the contact fingers engage a fixed contact to complete a circuit for effecting activation of the safety device, the mass being shown in' phantom lines in a fully actuated position in which the contact fingers are pressed more fully into engagement with the fixed contact;

FIG. 5 is a plan view taken approximately along the line 5- 5 of FIG. 4 further illustrating the sensor in its activated condition;

FIG. 6 is a schematic illustration of another embodiment of the present invention in which the sensor assembly includes shunting contacts for preventing accidental activation of the safety apparatus by induced currents; and

FIG. 7 is a schematic illustration of another embodiment of the sensor assembly.

The present invention provides a sensor assembly for detecting the occurrence of an accident and effecting actuation of a vehicle safety apparatus to protect an occupant of the vehicle. The sensor assembly includes a movable mass which is biased toward an initial position by a plurality of spring contact fingers. Upon the occurrence of an accident, the mass moves the spring fingers into engagement with a'fixed contact to complete a circuit and thereby effect activation of the safety apparatus.

Referring to FIG. 1, an automotive vehicle 20 is illustrated schematically and includes a safety apparatus 22. The safety apparatus 22 includes a confinement 24 which is expanded from a collapsed condition, shown in solid lines in FIG. 1, to an expanded condition, shown in dashed lines in FIG. 1, to restrain movement of an occupant 26 of the vehicle during an accident. While the confinement is illustrated in FIG. 1 as being located on the dashboard of the vehicle 20, it is contemplated that the confinement could be mounted on other parts of the vehicle, such as on the steering wheel, to prevent the driver of the vehicle from impacting with the steering wheel during an accident.

A sensor assembly 30 is connected with the safety apparatus 22 by electrical circuitry 32 and is operative to detect the occurrence of an accident and effect activation of the safety apparatus to its operative position shown in dashed lines in FIG. 1. In the present embodiment of the invention, the sensor assembly 30 is mounted on a fire wall 40 of the vehicle 20. Mounting the sensor asembly 30 on the fire wall 40 substantially isolates the sensor 30 from road vibrations which are normally induced to the frame 36 of the vehicle. Moreover, the sensor 30 will be subjected to deceleration during an accident which is similar to the deceleration to which the occupant is subjected so as to enable the mass 66 of the sensor to simulate the movement of an occupant during an accident.

The safety apparatus 22 includes a fluid supply, which in the present instance takes the form of a reservoir 44 of fluid under pressure. An explosive charge is associated with the reservoir 44, in a known manner, for forming an opening in the reservoir to enable the fluid to escape therefrom upon the occurrence of an accident. The explosive charge is detonated or activated by operation of the sensor assembly 30 upon the occurrence of an accident. Operation of the sensor assembly 30 completes a circuit from a source of power, such as a battery, through the sensor to the explosive charge to efiect activation of the explosive charge to efi'ect expansion of the confinement the accompanying 24. The confinement 24, in the expanded condition, restrains forward movement of the occupant 26 to prevent the occupant from engaging the windshield 60 or other parts of the vehicle under the influence of the forces of the accident.

The sensor assembly 30, as illustrated in FIGS. 2 and 3, includes a circular mass 66 supported in a housing 80 for movement relative thereto. The mass 66 is restrained against movement from an initial position or condition shown in FIGS. 2 and 3, to an actuated position or condition shown in FIGS. 4 and 5, by a plurality of resilient spring contact fingers 72. These contact fingers abuttingly engage the circular outer sur face 76 of the mass 66 when the mass is in the initial or inactive position shown in FIGS. 2 and 3. The occurrence of an accident effects deceleration of the vehicle 20 and of the housing 80 of the sensor assembly 30. The deceleration results in the mass 66 moving against the restraining effect of the yieldable contact fingers 72 so as to move the contact fingers into engagement with a semicircular fixed contact 84. Engagement of the contact fingers 72 with the fixed contact 84 completes an electrical circuit between the leads 48 and 49 and thereby effects operation of the safety apparatus 22.

The mass 66 is slidably supported by a generally horizontal surface 90 in a chamber 92 formed in the housing 80. A generally horizontal surface 91 is disposed immediately adjacent to and above the mass 66 and cooperates with the horizontal surface 90 to substantially prevent vertical movement of the mass 66. It should be apparent that the mass 66 may slide in a horizontal direction between the surfaces 90 and 91 but that vertical movement which might be induced to the mass due to vibration of the vehicle 20 will be prevented and the mass 66 will remain in a substantially horizontal position as illustrated in FIG. 2 at all times.

A pair of angularly related stop surfaces or walls 96 and 98 are provided in the housing for blocking the movement of the mass 66 in certain directions. The walls 96 and 98 and the horizontal surfaces 90 and 91 are all integrally formed with an upwardly projecting support or stop member 100. The stop surface against which the mass is biased by the spring fingers 72 and which comprises the walls 96 and 98 is formed from an energy absorbing material which preferably has a coefficient of restitution which is less than 0.4 so as to reduce the amount of rebound of the mass therefrom. The energy absorbing stop, which is more fully disclosed in the Kaiser and Goetz application, Ser. No. 753,946 filed Aug. 20, 1968, now US. Pat. No. 3,571,539, issued Mar. 23, 1971, and assigned to the assignee of the present invention, prevents inadvertent actuation of the mass due to vibrations induced from road conditions.

The walls 96 and 98 and the spring fingers 72 cooperate with the circular arcuate peripheral surface 76 of the mass 66 to impart spinning motion to the mass 66 when the mass moves against the stop surface after moving away from its initial position. This is due to the rolling contact of the circular peripheral surface 76 of the mass 66 with one of the walls 96 or 98 as the mass moves sidewardly along the walls toward the initial position of the mass and to the direction that the spring fingers 72 bias the mass. The spinning motion imparted to the mass 66 dissipates a portion of the kinetic energy from the mass as the mass returns to its initial position. Thus, when the mass moves due to noncollision conditions away from the initial position and then moves back to its initial position before moving to its actuated position, the spinning motion along with the energy absorbing capabilities of the walls 96 and 98 will dissipate kinetic energy of the mass and thereby prevent rebound of the mass from the stop surfaces. The force exerted by the contact fingers 72 varies according to the direction of impact on the vehicle due to the fact that when the mass 66 moves in different directions different numbers of contact fingers will act on the mass. For example, if the mass 66 moves to its actuated position illustrated in FIG. 5, a greater number of contact fingers will bias the mass toward its initial position than if the mass moved sidewardly along the wall 96 to its actuated position.

When the mass 66 tends to move forward under the influence of accident forces, the outer surface 76 of the mass 66 pivots certain of the contact fingers 72 relative to a base 102 of electrically conductive material from which the fingers 72 project. The base 102 of electrically conductive material is connected to the wire 49 and is integrally formed with the contact fingers 72. The base 102 is mounted between the support member and another support member 103 which cooperates to securely hold the base 102 in place. The support members 100 and 103 are made of electrically insulating material so as to prevent inadvertent actuation of the explosive associated with the fluid reservoir 44. The lead wire 49 connects the base 102 and the contact fingers 72 to the explosive associated with the fluid reservoir. The fixed contact 84 is connected with the wire 48 which extends to a power supply, such as the battery of the vehicle. Thus, when the mass 66 slides and presses the contact fingers 72 into engagement with the contact 84, a circuit is completed from the wire 48 through the fixed contacts 84 and movable contact 72 to the wire 49 to effect actuation of the explosive.

The contact fingers 72 perform two functions, that is, they act as a plurality of springs which are associated with the housing 80 and abuttingly engage with the circular surface 76 of the mass 66 to thereby restrain the mass 66 against movement from the initial position to an actuated position. The contact fingers 72 also function to complete an electrical circuit when they are moved into engagement with the fixed contact 84 by movement of the mass 66 relative to the housing 80.

The contact fingers 72 are disposed approximately 2l0 around the periphery of the mass 66 or in other words approximately in opposite directions from the forward direction of the vehicle 20. While the contact fingers 72 act as a plurality of springs, each of the contact fingers 72 acts individually of the other contact fingers 72. The number and specific fingers 72 that restrain the mass 66 from movement is dependent upon the direction that the mass 66 moves. Moreover, because the mass has a circular configuration as the mass 66 moves from its initial position to its actuated position, the number of spring fingers that act on the mass 66 will decrease as the spring fingers slide therefrom. This can easily be seen by comparing the number of spring fingers engaged with the mass in FIG. 3 to the number of spring fingers engaged with the mass in FIG. 5 when the mass is in its actuated position. The variation in the number of spring fingers which engage with the mass as the mass moves from its initial position to its actuated position and the effect of having a variable number of spring fingers which engage with the mass is more fully disclosed in the Kaiser application, Ser. No. 814,132 entitled CRASH SENSOR, filed Apr. 7, 1969, and assigned to the same assignee as the present invention. Moreover, it should be appreciated that movement of the mass 66 toward its actuated position effects spreading apart of the contact fingers 72. The spreading of the contact fingers 72 reduces friction between the contact fingers and the mass 66 as the mass moves toward its actuated position. This is a great improvement over prior art sensors which compress the contact fingers together as the mass moves toward its actuated position. When the contact fingers are compressed together, the friction between the contact fingers and the mass is increased with the result that the biasing force exerted on the mass will tend to increase.

The member 103 has a cam surface 104 formed integrally therewith which is disposed adjacent to the base of the contact fingers 72. When the vehicle encounters a head-on impact, the mass will move in the direction of the arrow A in FIG. 3 and the spring fingers will move therewith toward the fixed contact 84. As the mass moves toward its actuated position, the spring fingers will wrap around the cam 104 and the greater the movement of the mass 66 toward the fixed contact 84, the greater the wrap-up of the spring fingers 72 around the cam 104. This will cause the spring fingers 72 to each individually exert a slightly greater biasing force on the mass 66 and the biasing force exerted by each spring finger 72 will increase as the mass moves toward its actuated position. This is due to the fact that as the spring fingers wrap around the cam 104, the effective length of the spring fingers will decrease which will cause the spring constant of the spring fingers to increase somewhat. It should be apparent that because the spring constant increases somewhat as the distance that the mass moves from its initial position increases, the spring fingers will act as nonlinear springs and the force exerted by each finger 72 will increase nonlinearly as the distance through which the mass moves toward its actuated position increases. This is true because the force exerted by a spring is equal to the distance the spring is moved times the spring constant. Thus, if the distance increases while the spring constant increases, the force will increase nonlinearly. Thus, while fewer spring fingers are acting on the mass 66 as the mass moves toward its initial condition, due to the fact that some ofthe spring fingers will slide therefrom, the force exerted by the individual spring fingers on the mass will increase. The net result will be that the total force exerted on the mass will increase at a decreasing rate as the mass moves toward its actuated position.

While the present embodiment shows a cam 104 which cooperates with the spring fingers 72 so that the spring fingers 72 exert an increasing force on the mass as the mass moves to its initial position, it should be apparent that the configuration of the cam could be such that the force exerted by the spring fingers 72 could vary in other ways. For example, by making the slope of the cam smaller, a smaller portion of each of the spring fingers 72 would wrap up on the cam as the mass moves toward its actuated position and the force exerted on the mass by the aggregate of the spring fingers could be controlled so as to remain substantially constant as the mass moves toward its actuated position, even though some of the spring fingers will slide therefrom. Alternatively, by increasing the slope of the cam 104, the force exerted by the spring fingers 72 could be made to increase as the mass moves toward its actuated position.

it should also be appreciated that while the cam 104 is illustrated as having a constant cross-sectional configuration, a cam could be utilized having a varying cross-sectional configuration so as to vary the force exerted by each of the individual spring fingers 72. For example, if it is desired that the individual spring fingers which act on the mass when the mass moves in the sidewardly direction exert a greater force than the individual spring fingers which act on the mass when the mass moves in a forwardly direction as shown in FIG. 5, the slope of the cam 104 which would cooperate with the spring fingers 72 which are disposed sidewardly of the mass could be increased. Such a construction would allow the spring fingers disposed sidewardly of the mass 66 to individually exert greater forces on the mass 66 as the mass moves toward its actuated condition than the spring fingers disposed forwardly of the mass and which are contacted when the mass moves to its position shown in FIG. 5. By varying the slope of the cam 104 at different portions thereof, the biasing efiect which is exerted on the mass 66 by the spring fingers 72 can be controlled so that individual spring fingers 72 exert different biasing forces on the mass. Thus, the biasing force exerted on the mass would be dependent upon the direction the mass moves from its initial position if the cam 104 had a varying cross-sectional configuration. Moreover, the spring constant of the individual spring fingers 72 can be further varied by varying the width and thickness of the individual spring fingers. Thus, it should be obvious that the sensor assembly 30 can easily be constructed for use in many different types of vehicles which have different energy absorbing capabilities.

When the mass 66 moves the spring fingers 72 to their actuated position as is illustrated in full lines in FIG. 4, the top portion 72a of the spring fingers initially engages with the fixed contact 84. Due to the construction of the mass 66 and the spring fingers 72, a line contact will be made between the upper portion 72a on the spring finger 72 and the contact 84. However, the mass 66 has a certain amount of overtravel which causes the spring fingers 72 to wipe against the fixed contact 84. initially, only the upper portion 724 of the spring finger 72 engages with the fixed contact but further movement of the mass away from its initial position pushes the upper end 72a further toward the fixed contact 84. This causes the upper end 72a to wipe against and flatten out against the contact 84 to thereby increase the area of contact between the spring finger 72 and the fixed contact 84. As is illustrated in FIGS. 4 and 5 in phantom lines, the overtravel of the mass 66 causes the mass 66 to push a larger portion of the upper portion 72a of the spring finger 72 into contact with the fixed contact 84 as the mass travels an incremental distance past its actuated position. This overtravel of the mass and the further engagement of the contact 72 with the fixed contact 84 increases the duration of engagement between the movable contact 72 and the fixed contact 84 before the mass rebounds from the fixed contact 84. The increase in time, of course, increases the reliability of the sensor 30 due to the fact that the increased contact time between the movable contact 72 and the fixed contact 84 increases the time during which energy is applied to heat the explosive and thus prevents nonactuation of the explosive.

A proper relationship between the mass 66, the spring fin gers 72 and the distance of movement of the mass are necessary to enable the sensor assembly 30 to discriminate between various road conditions encountered by the vehicle and an accident. The movable contact fingers 72 are preferably moved through a distance of 0.50 of an inch when they are moved by the mass 66 into engagement with the fixed contact 84, but the distance could be as small as 0.1 of an inch or as large as 1 inch. During this movement, the contact fingers 72 exert a biasing force of approximately 8 gs which resist movement of the mass 66 from its initial condition. It has been generally found that if the distance through which the mass is moved from the initial position to the actuated position is less than 0.1 of an inch, the mass may be displaced to the actuated condition by severe road conditions causing an instantaneous high deceleration, even though the vehicle 20 has not encountered an accident. Generally, if the distance through which the mass 66 is displaced from the initial position to the actuated position is more than 1.0 inch, the time required for the mass to travel the distance will be so great as to prevent the confinement from being expanded at the proper time during an accident. If the biasing force of the spring against the mass is low, the mass will move under the influenceof the vibrations resulting from road conditions or braking. Of course, too high a biasing force would prevent or delay operation of the sensor assembly during certain accidents.

The spring constant of the individual spring fingers 72 and the configuration of the cam are chosen so that the mass 66 responds to an accident much in the same manner that the occupant responds. The mass 66 is operable to approximate the movement of the occupant but moves prior to the movement of the occupant so that the mass effects expansion of the confinement prior to movement of the occupant to the occupants collision position in which injury to the occupant would occur. This enables the mass 66 to efi'ect engagement of the spring finger 72 with the fixed contact 84 and thereby effect expansion of the confinement prior to the occupant impacting with portions of the vehicle.

While the distance through which the mass moves from its initial position to its actuated position is illustrated as being a constant distance, it should be apparent that a nonuniform contact gap could be provided between the fixed contact 84 and the spring fingers 72. The fixed contact 84 could be located closer to the spring fingers 72 at certain positions of the housing so that the force which would be required to move the mass to its actuated position and eflect engagement of the spring finger 72 with the fixed contacts 84 would be dependent not only upon the force exerted by the spring fingers 72 but also upon the spacing between the spring fingers 72 and the fixed contact 84 in the particular direction the mass moves. This is, of course, another way of compensating for the energy absorbing capabilities of the vehicle and varying the directional response of the sensor 30.

Moreover, it should be appreciated that more than one fixed contact 84 could be provided in the housing 80 so that more than one safety apparatus could be actuated. For example, if it is desired to actuate one safety apparatus when the mass moves in one direction and another safety apparatus when the mass moves in a different direction and it is not desired to operate both of the safety apparatuses simultaneously upon movement of the masses in either direction, then spaced apart fixed contacts could be provided so that movement of the mass in one direction would actuate one of the safety devices and movement of the mass in another direction would operate the other safety apparatus.

FIG. 6 schematically illustrates circuitry which may preferably be associated with the sensor 30 and which will enable the sensor 30 to effect actuation of the explosive charge associated with the fluid supply. As illustrated schematicaily in FIG. 6, the sensor assembly 30 is connected to a power supply such as the battery 110 and the ignition switch 112. However, an additional or redundant power supply could be connected with the sensor assembly 30 if desired for purposes of reliability. When the ignition switch is in its on position, as is illustrated in FIG. 6, a terminal 114 of the sensor is energized. A terminal 116 is located within the sensor and is spaced away from the terminal 114. When the mass moves to its actuated position, the movable contacts within the sensor will complete a circuit between the terminals 1 14 and 1 16.

The terminal 116 is connected by a lead 118 to one end of the explosive charges or detonators 120. The detonators 120 are preferably associated with a safety apparatus such as that illustrated in FIG. 1 located in the dashboard assembly of the vehicle 20. The other ends of the detonators 120 are connected via a lead 128 to a ground. It should be apparent that when the movable contact completes a circuit between the terminals 114 and 116, a current will flow through the explosive charges 120 to effect actuation thereof.

As shown schematically, a lead 122 is also associated with the terminal 1 l6 and is attached to the slip ring 124 of the type normally used on the horn of the vehicle and is associated with one end of a pair of explosive charges 126. The explosive charges 126 are grounded on their opposite end by a lead 130. The explosive charges 126 may preferably be associated with a safety apparatus which is located on the steering wheel assembly of the vehicle in a well known manner for restraining movement of the driver of the vehicle during the occurrence of an accident. It should be apparent that when the movable contacts 72 complete a circuit between the terminals 114 and 116, as is illustrated in broken lines in FIG. 6, current will flow through the detonators 126 and the detonators will effect expansion of the safety apparatus associated with the steering wheel assembly.

A pair of terminals 132 and 134 are electrically interconnected when the mass 66 is in its initial position. The terminal 132 is connected by a lead 138 to the lead 130 associated with the ground and the terminal 134 is connected by a lead 136 to the terminal 116. When a circuit is completed between the terminals 132 and 134, the ground 130 will be connected via the lead 136 to one side of the explosives 120 while the other side of the explosives 120 will be connected to the ground 128. Moreover, the explosives 126 will have both sides thereof connected to the ground 130, one side will be connected via the horn type slip rings 124 and the opposite side will be connected via a lead 140. Thus, any current that is induced into the circuitry will flow to the grounds rather than to the explosive means. Moreover, if radio frequency interference is picked up by the circuitry, this too will flow to the grounds rather than to the explosive means associated with the safety apparatus. Thus, inadvertent actuation of the safety apparatus will be prevented due to currents induced in the circuitry when the mass is in its initial position.

The schematic circuitry which is illustrated in FIG. 6 can be implemented in the sensor 30 shown in FIGS. 2 to 5 in many ways. For example, a pair of movable contacts could be located at the juncture between the walls 96 and 98 and when the mass is in its initial position as shown in FIG. 3, the mass 66 would bias the contacts to a closed position and complete a circuit between the terminals 132 and 134. Another convenient way of shunting the terminals 132 and 134 when the mass is in its initial position would be to provide a pair of spaced apart fixed contacts and 152 (FIG. 7) on the walls 96 and 98 and an annular contact ring 154 recessed in the surface 76 of the mass 66 and thereby isolated by contact with spring fingers 72. When the mass 66 is in its initial position, the circular contact disposed on the mass could complete a circuit between the contacts disposed on the walls 96 and 98 of the energy absorbing stop and, thus, a circuit would be completed between the terminals 132 and 134 to shunt the circuitry associated with the explosive devices. The contacts 150 and 152 on the walls 96 and 98 terminate midway along the walls so that when the mass 66 moves sidewardly to an actuated position, the contact ring 154 is spaced from the fixed contacts 150 and 152.

From the foregoing, it should be apparent that a new and improved sensor assembly has been provided for use with a safety apparatus for protecting an occupant of a vehicle. The sensor assembly includes a mass movable from an initial position to an actuated position in which the mass effects actuation of the safety apparatus. The mass is biased toward its initial position by a plurality of spring contact fingers. A cam member is associated with the contact fingers and cooperates therewith to deflect the contact fingers inwardly to apply a preload biasing force to the mass to thereby urge the mass toward the initial position. The cam member also increases the spring constants of the fingers somewhat as the fingers move with the mass toward its actuated position. However, the number of spring fingers engaging the mass decreases as the mass moves toward an activated position so that the force applied to the mass by the spring fingers increases at a decreasing rate as the mass moves toward its actuated position. Electrical circuitry is associated with the fixed and movable contact means to effect actuation of the safety apparatus when the mass moves to its actuated position. The electrical circuitry prevents inadvertent actuation of the safety apparatus when the mass is in its initial position.

What I claim is:

1. A sensor assembly comprising a housing, a mass located in said housing and movable between an initial position and an actuated position in response to an impulse of predetermined magnitude imposed upon said housing, contact means having open and closed conditions and being open when said mass is in said initial position and closing in response to said mass moving to said actuated position, and a plurality of spring fingers biasing said mass toward said initial position and applying a force to said mass which increases at a decreasing rate as said mass moves from said initial position toward said actuated position.

2. A sensor assembly as defined in claim 1 further including cam means mounted in said housing adjacent to said spring fingers for deflecting said spring fingers toward said mass to bias said mass toward the initial position.

3. A sensor assembly as defined in claim 2 wherein said spring fingers move in response to movement of said mass toward said actuated position, said cam means cooperating with said spring fingers upon movement of said mass toward said actuated position to decrease the effective length of said spring fingers as said mass moves toward said actuated position to thereby increase the spring rate of said spring fingers.

4. A sensor assembly as defined in claim 1 further including electrical circuitry associated with said contact means for actuating an explosive means upon closing of said contact means, and wherein said sensor assembly further includes means for grounding both sides of said explosive means when said mass is in said initial position to thereby prevent inadvertent actuation of said explosive means due to induced currents in said electrical circuitry.

5. A sensor assembly as defined in claim 3 wherein the number of said spring fingers which apply a biasing force to said mass decreases as said mass moves toward said actuated position.

6. A sensor assembly for use in actuating a safety apparatus on a vehicle for protecting an occupant of a vehicle during an accident, said sensor assembly comprising a housing adapted to be mounted on a vehicle, a movable mass located in said housing and having an initial position and an actuated position to which said mass moves in response to the occurrence of an accident, contact means having open and closed conditions and being open when said mass is in said initial position and closing in response to said mass moving to said actuated position, said closing of said contact means effecting actuation of the safety apparatus, spring means for biasing said mass toward said initial position, and means for varying the spring rate of said spring means as said mass moves between said initial and said actuated positions.

7. A sensor assembly comprising a housing, a mass located in said housing and movable between an initial position and an actuated position in response to an impulse of predetermined magnitude impoud upon said housing, contact means having open and closed conditions and being open when said mass is in said initial position and closing in response to said mass moving to said actuated position, a plurality of spring fingers, and cam means for resiliently deflecting said spring fingers toward and into pressure engagement with said mass when said mass is in the initial position to apply a biasing force to said mass.

8. A sensor assembly as set forth in claim 7 wherein said contact means includes first contacts and second contacts on said spring fingers, said mass being movable under the influence of the impulse of predetermined magnitude and against the biasing force to further deflect the spring fingers and move said second contacts into initial engagement with said first contacts and to move said second contacts relative to said first contacts with a wiping action to promote the establishment of an electrical interconnection between said 1 first and second contacts.

'0' I? It I l 

1. A sensor assembly comprising a housing, a mass located in said housing and movable between an initial position and an actuated position in response to an impulse of predetermined magnitude imposed upon said housing, contact means having open and closed conditions and being open when said mass is in said initial position and closing in response to said mass moving to said actuated position, and a plurality of spring fingers biasing said mass toward said initial position and applying a force to said mass which increases at a decreasing rate as said mass moves from said initial position toward said actuated position.
 2. A sensor assembly as defined in claim 1 further including cam means mounted in said housing adjacent to said spring fingers for deflecting said spring fingers toward said mass to bias said mass toward the initial position.
 3. A sensor assembly as defined in claim 2 wherein said spring fingers move in response to movement of said mass toward said actuated position, said cam means cooperating with said spring fingers upon movement of said mass toward said actuated position to decrease the effective length of said spring fingers as said mass moves toward said actuated position to thereby increase the spring rate of said spring fingers.
 4. A sensor assembly as defined in claim 1 further including electrical circuitry associated with said contact means for actuating an explosive means upon closing of said contact means, and wherein said sensor assembly further includes means for grounding both sides of said explosive means when said mass is in said initial position to thereby prevent inadvertent actuation of said explosive means due to induced currents in said electricaL circuitry.
 5. A sensor assembly as defined in claim 3 wherein the number of said spring fingers which apply a biasing force to said mass decreases as said mass moves toward said actuated position.
 6. A sensor assembly for use in actuating a safety apparatus on a vehicle for protecting an occupant of a vehicle during an accident, said sensor assembly comprising a housing adapted to be mounted on a vehicle, a movable mass located in said housing and having an initial position and an actuated position to which said mass moves in response to the occurrence of an accident, contact means having open and closed conditions and being open when said mass is in said initial position and closing in response to said mass moving to said actuated position, said closing of said contact means effecting actuation of the safety apparatus, spring means for biasing said mass toward said initial position, and means for varying the spring rate of said spring means as said mass moves between said initial and said actuated positions.
 7. A sensor assembly comprising a housing, a mass located in said housing and movable between an initial position and an actuated position in response to an impulse of predetermined magnitude imposed upon said housing, contact means having open and closed conditions and being open when said mass is in said initial position and closing in response to said mass moving to said actuated position, a plurality of spring fingers, and cam means for resiliently deflecting said spring fingers toward and into pressure engagement with said mass when said mass is in the initial position to apply a biasing force to said mass.
 8. A sensor assembly as set forth in claim 7 wherein said contact means includes first contacts and second contacts on said spring fingers, said mass being movable under the influence of the impulse of predetermined magnitude and against the biasing force to further deflect the spring fingers and move said second contacts into initial engagement with said first contacts and to move said second contacts relative to said first contacts with a wiping action to promote the establishment of an electrical interconnection between said first and second contacts. 